Assuring Bridge Safety and Serviceability in Europe

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Executive Summary

• Background
• Summary of Initial Findings
• Recommendations
• Implementation Activities

Chapter One: Introduction

• Background
• Scan Team
• Amplifying Questions
• Host Countries

Chapter Two: Findings on Assuring Bridge Safety and Serviceability

• Eurocodes
• Background
• Vehicular Live Loads and Live Load Factors
• Refined Methods of Analyzing, Designing, and Assessing Bridges
• Finite Element Analysis of New Bridges
• Finite Element Analysis of Existing Bridges
• Weigh–in–Motion Data
• Use of Enhanced Reliability Analysis to Assess Safety
• Quantification of Safety
• Bridge Operations
• Quality Assurance/Quality Control
• Design Checks
• Inspection
• Laser Scanning
• QA/QC in the United Kingdom
• Processes and Practices to Provide serviceability and Durability

Chapter Three: Recommendations and Implementation Activities

• Recommendations
• Implementation Activities

Appendix A: Amplifying Questions

Appendix B: Scan Team members

Appendix C: Host country contacts

Appendix D: Finnish statistical Process controls in the bridge Inspection Program

Figures

• Figure 1. Scan team members
• Figure 2. Hierarchy of Eurocodes on concrete bridge design
• Figure 3. German live load
• Figure 4. Finnish live load used for rating
• Figure 5. Change management
• Figure 6. Weigh–in–motion data
• Figure 7. Contractual relationship of the check engineer
• Figure 8. Finnish statistical process control
• Figure 9. Laser scanning of structures in Finland
• Figure 10. Detail of drag plate used in austrian integral bridges
• Figure 11. Crack width control
• Figure 12. External post–tensioning
• Figure 13. Typical two–girder system in Europe
• Figure 14. Maximum allowed values for the deviation Pl and relative deviations SP and SPkust
• Figure 15. Plot of divergence indicator from Finnra quality reports
• Figure 16. Example calculation of Finnra quality parameters

Tables

• Table 1. Scan itinerary
• Table 2. Eurocode consequence classes
• Table 3. Inherent probabilities of failure (Pf) and corresponding reliability indices (ß)
• Table 4. Quality control inspections in 2005

Abbreviations and Acronyms

AASHTO

American Association of State Highway and Transportation Officials

ASFiNAG

Autobahnen– und Schnellstraßen– Finanzierungs– Aktiengesellschaft

BASt

Bundesanstalt für Straßenwesen (Federal Highway Research Institute)

CTOA

Centre Technique des Ouvrages d’Art

DOT

Department of transportation

EU

European Union

FEM

finite element method

FHWA

Federal Highway Administration

Finnra

Finnish Road Administration

GIS

geographic information system

HA

Highways Agency

HGV

heavy goods vehicle

LCPC

Laboratoire Central des Ponts et Chaussées

LRFD

load and resistance factor design

LRFR

load and resistance factor rating

MR&R

maintenance repair and rehabilitation

NBIS

National Bridge Inspection Standards

NCHRP

National Cooperative Highway Research Program

NDE

nondestructive evaluation

NDPs

Nationally Determined Parameters

QA/QC

quality assurance/quality control

Sétra

Service d’Etudes Techniques des Routes et Autoroutes

TRB

Transportation Research Board

WIM

weigh–in–motion

Executive Summary

Background

U.S. engineers need new, advanced tools and protocols to better assess and assure safety and serviceability of highway bridges. These tools include an overall, integrated approach to bridge analysis, design, evaluation, and load-carrying capacity (load rating). Present-day design specifications (load and resistance factor design (LR FD)) have assured safety by analyzing the effect of heavy, legal trucks throughout the United States and applying calibration protocol using limited Canadian site statistics. However, the calibration did not include serviceability calibration to assure bridge serviceability and performance. Therefore, it is desirable to identify design practices, design truck assessments, and detailed code calibration procedures used in other countries to assure the safety and serviceability of newly designed bridges.

The new American Association of State Highway and Transportation Officials (AASHTO) Manual for Bridge Evaluation was developed to assist bridge owners by establishing inspection, evaluation, load rating, and posting practices and procedures. The load and resistance factor rating (LRFR) section of the manual is based on reliability theories to assure a certain level of safety for members. However, certain serviceability checks were left optional because they are not directly related to bridge safety, but are geared to protecting the long-term serviceability and durability of structures. It is unclear whether making these checks optional has an effect on the service life of aging U.S. bridges. Therefore, it is desirable to identify evaluation (load-carrying assessment) best practices and quantify the required level of safety and performance used in other countries to avoid failures, serviceability concerns, unnecessary expenditures, and traffic restrictions.

Knowledge and software have evolved to enable moving away from line girder approximate procedures to a system approach using advanced finite element analyses. However, current U.S. specifications and practice still, for the most part, rely on simplified, approximate analyses to determine the structural effects of vehicular loading on bridge girders. Situations impeding the use of advanced analysis in design and evaluation include the cost of software, lack of training, lack of guidance materials, modeling complexities, and perceived high cost-to-benefit ratio. A growing number of U.S. bridge owners and engineers seek to expand and mainstream the use of more rigorous design and evaluation approaches in everyday practice to achieve more economical use of materials, a better understanding of the structural system, and a better quantified level of safety and serviceability.

The purpose of the scan was to identify best practices and processes to assure bridge safety and serviceability for implementation in the United States. Specific topics of interest included the following:

• Safety and serviceability—design and construction
• Safety and serviceability—operations
• Refined analysis—design, construction, and operations

The team developed a comprehensive list of technical and operational process questions, including topics on safety and serviceability concerns and the use of refined analysis during the design, construction, and operational phases of a bridge’s life (Appendix A).

An 11-member team was formed to conduct the study. This team consisted of three representatives from the Federal Highway Administration (FHWA), four representatives from State departments of transportation, one representative from academia, and three structural engineering design consultants, one who served as the report facilitator.

The team conducted a series of meetings and site visits with representatives of government agencies and private sector organizations abroad from May 29 to June 14, 2009. The team visited Austria, England, Finland, France, and Germany. These five countries were selected through a desk scan that identified their use of advanced activities in assuring bridge safety and serviceability.

Summary of Initial Findings

The scan team found that, as in the United States, the European host agencies put a tremendous value on bridge programs not only to ensure highway user safety, but also to ensure that durability and serviceability expectations are met and to enhance capital investment decisions on the existing bridge inventory. They place major emphasis on ensuring that there is no service interruption because of a bridge failure or major repair, and that appropriate sophisticated methods are used to evaluate structural safety. Most of the agencies visited had major programs aimed at assuring accuracy of design and rating of highway structures on their systems.

The scan team also identified many practices and technologies related to the topics of interest. The order in which they are presented in this report is for clarity of presentation and does not reflect the priority recommended by the team.

Recommendations

Based on the above findings, the recommendations of the team are as follows:

1. Develop a nationally accepted strategy for promoting and increasing the practicing bridge engineer’s use of refined analysis for design and evaluation.
2. Encourage states to use refined analysis for evaluation in combination with reliability analysis to avoid unnecessary posting, rehabilitation, or replacement of bridge structures.
3. Encourage the AASHTO subcommittee on bridges and structures to adopt the concept of annual probability of failure (exceedance) as the quantification of safety in its probability-based design and rating specifications rather than the reliability index for a 75-year design life.
4. Conduct research to create the basis to systematically introduce increasing levels of sophistication into analyses and load models with the objective of assessing bridges more accurately.
5. encourage owners to periodically and routinely reassess traffic highway loading, using recent weighin-motion data, to ensure that their live load model adequately provides for bridge safety and serviceability for the desired service life and level of safety.
6. Encourage states to develop an overweight permit design vehicle and design for the associated AASHTO strength II load combination, the load combination meant to consider special permit truck loads during the design of a bridge, particularly in high-load corridors.
7. Initiate and maintain a database documenting bridge failures around the world, including sufficient information and data to assist in assessing the causes of failure, for the purpose of proactively examining U.s. practices and avoiding similar problems in the United states.
8. continue efforts to develop guidelines and training for proper use of nondestructive techniques to detect corrosion and breakage of cables of cable-supported bridges and internal and external tendons of posttensioned bridges.
9. explore independent check engineering and check engineer certification to augment quality assurance and quality control of bridge designs.
10. Initiate an investigation and technology transfer of selected best practices and emerging technologies identified during the scan. Potential candidates are outlined in this report.

Implementation Activities

The scan team developed a detailed implementation plan for the recommended initiatives and practices. Included in the plan are technical presentations and written papers at national meetings and conferences sponsored by FHWA, ASSHTO, the Transportation research board, and other organizations to disseminate information from the scan. also included in the plan is coordination with AASHTO and FHWA to advance these initiatives and practices and to assist with the development of new FHWA and AASHTO standards and guidelines governing bridge design and analysis. These and other planned activities are discussed in chapter 3.